Methods for making data storage media and the resultant media

ABSTRACT

Methods for forming data storage media and the media formed thereby are disclosed herein. In one embodiment, the method for forming a data storage media, comprises: injection molding a substrate comprising surface features, wherein said surface features have greater than about 90% of a surface feature replication of an original master; and disposing a data layer over at least one surface of said substrate; wherein said data storage media has an axial displacement peak of less than about 500μ under shock or vibration excitation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 09/846,888 filed May 1, 2001, now U.S. Pat. No. 6,715,200 whichclaims the benefit of the filing date of U.S. Provisional ApplicationSer. Nos. 60/120,101 filed Feb. 12, 1999; 60/134,585 filed May 17, 1999;60/137,883 filed Jun. 7, 1999; and 60/137,884 filed Jun. 7, 1999;60/146,248 filed Jul. 29, 1999; and which is a divisional of U.S.application Ser. No. 09/502,968 filed Feb. 11, 2000 now abandoned; theentire contents of each application are hereby incorporated byreference.

FEDERALLY SPONSORED RESEARCH

Not Applicable

TECHNICAL FIELD

The present disclosure relates to data storage media and methods formaking such media, and especially relates to methods of making datastorage media and to partially and wholly plastic data storage media.

BACKGROUND OF THE INVENTION

Optical, magnetic and magneto-optic media are primary sources of highperformance storage technology, which enables high storage capacitycoupled with a reasonable price per megabyte of storage. Areal density,typically expressed as billions of bits per square inch of disk surfacearea (Gbits per square inch (Gbits/in²)), is equivalent to the lineardensity (bits of information per inch of track) multiplied by the trackdensity in tracks per inch. Improved areal density has been one of thekey factors in the price reduction per megabyte, and further increasesin areal density continue to be demanded by the industry.

In the area of optical storage, advances focus on access time, systemvolume, and competitive costing. Increasing areal density is beingaddressed by focusing on the diffraction limits of optics (usingnear-field optics), investigating three dimensional storage,investigating potential holographic recording methods and othertechniques.

Conventional polymeric data storage media has been employed in areassuch as compact disks (CD-ROM) and recordable or re-writable compactdisks (e.g., CD-RW), and similar relatively low areal density devices,e.g. less than about 1 Gbits/in², which are typically read-throughdevices requiring the employment of a good optical quality substratehaving low birefringence.

Referring to FIG. 1, a low areal density system 1 is illustrated havinga read device 3 and a recordable or re-writable storage media 5. Thestorage media 5 comprises conventional layers, including a data layer 7,dielectric layers 9 and 9′, reflective layer 11, and protective layer13. During operation of the system 1, a laser 15 produced by the readdevice 3 is incident upon the optically clear substrate 17. The laserpasses through the substrate 17, and through the dielectric layer 9, thedata layer 7 and a second dielectric layer 9′. The laser 15 thenreflects off the reflective layer 11, back through the dielectric layer9′, the data layer 7, the dielectric layer 9, and the substrate 17 andis read by the read device 3.

Unlike the CD and beyond that of the DVD, storage media having highareal density capabilities, typically greater than 5 Gbits/in², employfirst surface or near field read/write techniques in order to increasethe areal density. For such storage media, although the optical qualityof the substrate is not relevant, the physical and mechanical propertiesof the substrate become increasingly important. For high areal densityapplications, including first surface applications, the surface qualityof the storage media can effect the accuracy of the reading device, theability to store data, and replication qualities of the substrate.Furthermore, the physical characteristics of the storage media when inuse can also effect the ability to store and retrieve data; i.e. theaxial displacement of the media, if too great, can inhibit accurateretrieval of data and/or damage the read/write device.

Conventionally, the above issues associated with employing firstsurface, including near field, techniques have been addressed byutilizing metal, e.g., aluminum, and glass substrates. These substratesare formed into a disk and the desired layers are disposed upon thesubstrate using various techniques, such as sputtering. Possible layersinclude reflective layers, dielectric layers, data storage layers andprotective layers. Once the desired magnetic layers have been added, thedisk may be partitioned into radial and tangential sectors throughmagnetic read/write techniques. Sector structure may also be addedthrough physical or chemical techniques, e.g. etching, however this mustoccur prior to the deposition of the magnetic layers.

As is evident from the fast pace of the industry, the demand for greaterstorage capacities at lower prices, the desire to have re-writabledisks, and the numerous techniques being investigated, further advancesin the technology are constantly desired and sought. What is needed inthe art are advances in storage media substrate materials enablingstorage media to be utilized in first surface, including near field,applications.

BRIEF SUMMARY OF THE INVENTION

Methods for forming data storage media and the media formed thereby aredisclosed herein. In one embodiment, the method for forming a datastorage media comprises: forming a substrate; disposing a plastic layeron at least one surface of a substrate; embossing the plastic layer byheating a first substrate to a temperature above a substrate surfaceglass transition temperature, preheating and maintaining a mold at amold temperature below said substrate surface glass transitiontemperature, introducing said heated substrate to said preheated mold,compressing said heated substrate in said mold, cooling said compressedsubstrate, and removing said cooled substrate from said mold; anddisposing a data layer over said plastic layer; wherein said datastorage media has an axial displacement peak of less than about 500μunder shock or vibration excitation.

In another embodiment, the method for forming a data storage media,comprises: forming a substrate; disposing a plastic layer on at leastone surface of a substrate; embossing the plastic layer by heating afirst substrate to a temperature above a substrate surface glasstransition temperature, preheating a mold to a mold temperature of up toabout 30° C. above said substrate surface glass transition temperature,introducing said heated substrate to said preheated mold, compressingsaid heated substrate in said mold, cooling said compressed substrate,and removing said cooled substrate from said mold; and disposing a datalayer over said plastic layer; wherein said data storage media has anaxial displacement peak of less than about 500μ under shock or vibrationexcitation.

In yet another embodiment, the method for forming a data storage media,comprises: injection molding a substrate comprising surface features,wherein said surface features have greater than about 90% of a surfacefeature replication of an original master; and disposing a data layerover at least one surface of said substrate; wherein said data storagemedia has an axial displacement peak of less than about 500μ under shockor vibration excitation.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional illustration of a prior art low arealdensity system employing an optically clear substrate.

FIG. 2 is a cross-sectional illustration of a read/write system usingone possible embodiment of a storage media of the present invention witha light incident on the data storage layer without passing through thesubstrate.

FIG. 3 is a cross-sectional illustration of one embodiment of a magneticdata storage substrate of the present invention.

FIG. 4 is a graph of flexural modulus versus specific gravity forvarious fundamental axial modal frequencies of a monolithic disk havinga 95 mm outer diameter by 0.8 mm thickness.

FIG. 5 is a graph of specific stiffness (flexural modulus divided byspecific gravity) versus damping coefficient for various peak to peakaxial displacements when excited by a 1 G sinusoidal load.

FIG. 6 is a graph representing the fundamental axial modal frequency fora multi layered composite 130 mm outer diameter by 1.2 mm thickness diskwith homogeneous layers of neat and reinforced polymer.

FIG. 7 is graph representing axial displacement peak to peak fromvibration at the first fundamental frequency for a multi-layeredcomposite (ABA co-injected disk) 130 mm outer diameter by 1.2 mmthickness disk having homogeneous layers of neat and reinforced polymer.

FIGS. 8 to 21 illustrate various cross-sectional and top views ofembodiments of the present invention having a core/insert of material,or hollow or filled cavities, with the core/insert disposed at variouslocations, with various geometries.

FIG. 22 is an embodiment similar to FIG. 19 illustrating anon-homogenous (ABA) substrate with pits or grooves.

FIGS. 23 and 24 are cross-sectional views of additional embodiments ofthe present invention illustrating a substrate having thin plastic film.

FIG. 25 is a cross-sectional view of one embodiment of a tri-componentdisk of the present invention.

FIG. 26 is a cross-sectional view of another embodiment of a disk of thepresent invention secured with a clamp.

FIG. 27 is a cross-sectional view of yet another embodiment of thepresent invention having a thin plastic film disposed on a portion of acore.

FIGS. 28 to 32 illustrate various embodiments of possible substrategeometries for the substrate of the present invention.

FIGS. 33 to 35 illustrate various embodiments of possible coregeometries for the storage media of the present invention.

FIG. 36 illustrates modal shapes obtained from with a 130 mm disk viachirp excitation.

The above-described Figures are meant to be exemplary, not limiting,merely illustrating some of the potential embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The data storage media is partially or wholly comprised of a plasticmaterial. This storage media is useful in high areal densityapplications, first surface and similar applications, wherein an energyfield incident on the data storage layer(s) contacts the data storagelayer(s) without or at least prior to contacting the substrate. In otherwords, in contrast to conventional compact disks (CDs) and similarapplications, the energy field does not pass through the substrate tocontact the data storage layer or reflect back through the substrate tothe reading device. In order to function in such high areal densityapplications the storage media quality must exceed that of conventionalCDs and related media. The storage media, compared to conventional CDsand similar media, should have a reduced axial displacement when excitedby environmental and/or rotational vibrations, greater surface qualitydenoted by fewer irregularities or imperfections, and lower rotatingmoment of inertia (preferably about 5.5×10⁻³ slug-in² or less, withabout 4.5×10³¹ ³ slug-in² or less more preferred, and about 4.0×10⁻³slug-in² or less especially preferred), among other qualities.Furthermore, the storage media preferably comprises areal densitiesexceeding about 5 Gbits/in², with greater than about 20 Gbits/in² morepreferred, greater than about 50 Gbits/in² especially preferred, and upto or exceeding about 100 Gbits/in² anticipated.

Generally, in high areal density applications, i.e. about 5 Gbits/in² orgreater, the read/write device is located relatively close to thesurface of the storage media (stand-off distance). In general, thehigher the density sought, the closer the read/write device should be tothe surface of the storage media. Typically in these instances, thestand-off distance is generally less than about 0.3 millimeters (mm),and often less than about 760 nanometers (nm). For extremely highdensity, the read/write device is preferably extremely close, e.g., lessthan about 0.064 micrometers (μ), often less than about 0.013μ from thesurface. Consequently, the axial displacement of the substrate should besufficiently less than a tolerable system deflection distance in orderto prevent damage to the read/write device and/or storage media surfaceduring vibration and/or shock conditions. For example, for a disk (130mm in outer diameter, 40 mm in inner diameter, and 1.2 mm in thickness)experiencing a sinusoidal gravitational loading of about 1 G, a resonantfrequency of about 170 Hz, and a stand-off distance of about 0.051μ, anaxial displacement in peak to peak measurement of less than about 250μis preferred, with less than about 150μ more preferred, and less thanabout 125μ especially preferred for instances when damage to thesubstrate and/or the read/write device is a primary concern. Preferably,an axial displacement in peak to peak measurement of about 500μ or less,with about 250μ or less preferred, is maintained to a shock maximum ofabout 25 G's, with an about 2 to about 10 milliseconds (msec)application time and maintaining such a displacement to about 35 G'spreferred. However, in other instances, e.g., those with a largerstandoff distance (e.g., the about 0.30μ or more stand-off) damage tothe head is not a dominating issue but rather, a very low axialdisplacement and/or disk tilt is preferred to allow for the optics toremain in focus since they may be incapable of responding to rapidchanges in focal length. The maximum radial tilt and tangential tilt areindependently about 1° or less, preferably, no more than about 1° each,and more preferably less than about 0.3° each, measured in a restingstate (i.e., not spinning).

The substrate axial displacement is a function of severalcharacteristics, including, but not limited to, the disk sizerequirements (inner and outer radii, and thickness), its stiffness(flexural modulus) and density, Poisson's ratio, loss modulus andstorage modulus, and combinations thereof and others. As the disk'souter radius increases, the axial displacement of the disk under shockand vibration conditions also increases, and as the disk thicknessdecreases, its sectional stiffness decreases while its axialdisplacement increases. Currently, the dimensions of the storage mediaare specified by the industry to enable their use in presently availablestorage media reading/writing devices. Consequently, the storage mediatypically has an inner diameter of up to about 40 millimeters (mm) andan outer diameter of up to about 130 mm or greater, with an innerdiameter of about 15 mm to about 40 mm and an outer diameter of about 65mm to about 130 mm generally employed. The overall thickness typicallyemployed is about 0.8 mm to about 2.5 mm, with a thickness up to about1.2 mm typically preferred. Other diameters and thicknesses could beemployed to obtain the desired architecture.

In addition to axial displacement, stiffness affects the fundamentalfrequencies for vibration of the substrate. It has been determined thatthe occurrence of the fundamental modal frequency can be adjusted basedupon several factors, including material properties, e.g., the flexuralmodulus, thickness, and/or the specific gravity (S. G.)/density of thesubstrate or design architecture, e.g. internal/external stiffeners.(See FIG. 4) Since the modal frequencies define the frequency at whichthe substrate naturally resonates, displacing the disk out of plane, itis preferred to have the substrate's first modal frequency outside ofthe storage media's normal operating frequency. Normal operatingfrequencies are typically about 20 Hz to about 500 Hz, with greater than500 Hz anticipated for future applications. Consequently, the substratepreferably possesses a flexural modulus/density which places the firstmodal frequency outside of the storage media's operating frequency. Asis evident from FIG. 4 (whose properties are set forth in the Tablebelow) the interrelationship of flexural modulus and specificgravity/density greatly effects the desired substrate flexural modulusand density. Preferably, the stiffness should be high and the densityshould be low. Typically, the flexural modulus should be about 250thousand pounds per square inch (kpsi) or greater, with a flexuralmodulus of about 350 kpsi or greater preferred, about 500 kpsi orgreater more preferred, and a flexural modulus of about 1000 kpsi orgreater especially preferred, while the specific gravity is preferablyabout 1.5 or less, with a specific gravity of about 1.3 or less morepreferred, and a specific gravity of about 1.0 or less especiallypreferred.

As with the axial displacement, due to the small stand-off distancesemployed and the deleterious effect of surface roughness oncarrier-to-noise ratio, the substrate should have a high surfacequality, particularly in the area of the storage media where the data isstored, and should be substantially flat to inhibit damage to theread/write device or surface of the storage media, and to enableaccurate data deposit and retrieval. Preferably, the substrate has atleast a portion of its surface with an average surface roughness((R_(a)) as measured by atomic force microscopy) of less than about 100Angstroms (Å), preferably with a roughness of less than about 10 Å, andmore preferably with a roughness of less than about 5 Å. (Roughness istypically an average of a 10μ by 10μ area of the substrate.) Themicrowaviness of the surface, which is typically an average of a 1 mm by1 mm area, can be up to about 100 Å, with up to about 10 Å preferred,and up to about 5 Å especially preferred. With respect to the flatness(also known as “run-out”), a substantially flat substrate essentiallyfree of ridges or valleys, is especially preferred. A run-out of up toabout 100μ can be employed, with a run-out of up to about 10μ preferred,and a run-out up to about 5μ especially preferred. (Flatness istypically an average of the area of the entire disk.)

At such small stand-off distances, a ridge at or near the edge of thesubstrate, commonly known as edge-lift or ski-jump, can cause damage tothe read/write device. The substrate should have a edge-lift height ofless than about 8μ, with less than about 5μ preferred, and less thanabout 3μ especially preferred, with a edge-lift length of less thanabout 800μ preferred, and less than about 500μ especially preferred.

The storage media can be used in a variety of systems, some of whichwill employ a restraining device necessitating consideration ofstiffness decay of the substrate. For a read/write system which employsa clamp, hub, or other restraining device to secure the storage media,the substrate should have a sufficient yield stress (at least in thecontact area of the restraining device) to avoid mechanical decay (bothbased upon time and/or temperature). For a storage media having an outerdiameter of about 65 mm to about 130 mm, that will be secured within arestraining device of a read/write system, the plastic resins to be usedhave a preferred yield stress of about 7,000 psi or greater, with ayield stress exceeding about 9,000 psi especially preferred. In the caseof filled engineering plastic resins, higher yield stresses areobtainable, and yield stress exceeding about 10,000 pounds per squareinch (psi) are preferred, with greater than about 15,000 psi especiallypreferred.

Some such disks are illustrated in FIGS. 25 to 27. FIG. 25 illustrates adisk 200 having a polymer surface 202, a filled or hollow core 204, witha central portion 206 of a material comprising a higher yield stressthan the plastic 202, such as a metal (e.g., aluminum), glass, ceramic,metal-matrix composite, and alloys and combinations comprising at leastone of the foregoing, and the like. FIG. 26 illustrates a disk having ahigh yield stress central portion 206 attached to a clamp 208.Meanwhile, FIG. 27 illustrates yet another embodiment wherein thepolymer is a thin film over a core 204′ composed of the same material asthe central portion 206. For example, the core can be metal with aplastic film 202 disposed over a portion or all of the core.

Conventional substrates, e.g., aluminum and ceramic substrates without aplastic overlay, have a very high stiffness (e.g., aluminum with aYoung's modulus of about 70 gigapascals (GPa), and ceramic with aYoung's modulus of about 200 GPa), a level above that which has beenachieved with plastic substrates. It was unexpectedly found that thedamping coefficient of a material is important to offset the decreasedstiffness of plastic substrates as compared to aluminum. Consequently,in order to minimize effects of vibration of the disk, the visco-elasticmaterial properties of the substrate can be adjusted to enable dampingcapabilities. Vibration damping is achieved in a general sense, forexample, by inserting an appropriate spring/dashpot assembly between avibration source and an object to be vibrated. For effective damping,the material should absorb and/or dissipate the energy of vibrationtransmitted through the material as energy (e.g., heat energy) convertedas a result of planar shearing or bulk compression and expansion of thematerial.

For visco-elastic materials, such as plastic resins, there exists both astorage modulus and a loss modulus. Storage modulus represents elasticstiffness and loss modulus represents viscous stiffness. For a storagemedia having a stiffness less than aluminum, it is preferred that thesubstrate have a mechanical damping coefficient (defined as the ratio ofthe loss modulus over the storage modulus) of greater than about 0.04 ata temperature of 75° F. (about 24° C.), with greater than about 0.05preferred, and greater than about 0.06 more preferred. A mechanicaldamping coefficient of greater than about 0.10 at a temperature of 75°F. is even more preferred, and a mechanical damping coefficient ofgreater than about 0.15 at a temperature of 75° F. is especiallypreferred.

In addition, the damping properties of the material may be optimizedsuch that, for a frequency and temperature range of interest, thedamping coefficient value does not drop below the desired value. In someembodiments, the temperature range of interest and frequency range forapplicability of the dampening is about 75° F. (24° C.) and about 2 Hzto about 150° F. (65.5° C.) and about 400 Hz preferred, with about 32°F. (0° C.) and about 2 Hz to about 200° F. (93.3° C.) and about 500 Hzmore preferred.

FIGS. 5 and 7 represent the relationship between axial displacement fora 1 G sinusoidal vibration load for various material properties andfixed geometries. FIG. 6 shows that the damping coefficient does noteffect the first modal frequency while FIG. 7 shows the effects of axialdisplacement on the first modal frequency.

Mechanical Input Properties for 130 mm ABA Co-Injected Disk StorageModulus Damping Poisson's Structure Material (psi) Coefficient RatioS.G. Skin Neat Resin 3.15E+05 0.033 0.385 1.200 Core Filled 1.25E+060.040 0.375 1.315 System 1.25E+06 0.060 0.375 1.320 1.25E+06 0.080 0.3751.325 1.25E+06 0.100 0.375 1.330

Damping, also referred to as dampening, can be achieved through avariety of approaches such as by addition of an energy absorbingcomponent or through slip mechanisms involving various fillers andreinforcing agents. Useful materials that may improve the dampingcharacteristics include elastic materials with high damping capabilities(e.g., a damping coefficient of greater than about 0.05), such asvulcanized rubbers, acrylic rubbers, silicone rubbers, butadienerubbers, isobutylene rubbers, polyether rubbers, isobutylene-isoprenecopolymers and isocyanate rubber, nitrile rubbers, chloroprene rubbers,chlorosulfonated polyethylene, polysulfide rubbers and fluorine rubber,block copolymers including polystyrene-polyisoprene copolymers such asdescribed in U.S. Pat. No. 4,987,194 (which is incorporated herein byreference), thermoplastic elastomeric materials, includingpolyurethanes, and combinations comprising at least one of theforegoing, among others. Vibration-damping materials also include resinsin which large amounts of particles (such as ferrites, metals, ceramicsand the like), flakes (such as of talc, mica and the like), and variousfibers (such as zinc oxide, wollastonite, carbon fibers, glass fibers,and the like), and mixtures comprising at least one of the foregoing,can be employed. Microfibers, fibrils, nanotubes, and whiskers, foamedand honeycombed structures may also be useful as are variouscombinations of the foregoing.

In addition to, or in place of, reducing axial displacement through theuse of damping materials in the substrate, axial displacement can bereduced by utilizing a vibration damping material in the restrainingdevice, or clamping structure, that holds the substrate. The addition ofvisco-elastic materials to the clamp or between the clamp and substrateeffectively reduces axial displacement of the disk compared to the samestructure without the additive. In one embodiment, the vibration-dampingmaterial should preferably have a damping coefficient higher than thedamping coefficient of the disk substrate, and a modulus of elasticityhigh enough to reduce creep properties, e.g., a modulus of elasticitygreater than about 20 kpsi. Useful materials that may improve thedamping characteristics of the clamp include elastic materials with highdamping capabilities, such as vulcanized rubbers, acrylic rubbers,silicone rubbers, butadiene rubbers, isobutylene rubbers, polyetherrubbers, isobutylene-isoprene copolymers and isocyanate rubber, nitrilerubbers, chloroprene rubbers, chlorosulfonated polyethylene, polysulfiderubbers and fluorine rubber, block copolymers includingpolystyrene-polyisoprene copolymers such as described in U.S. Pat. No.4,987,194, thermoplastic elastomeric materials, including polyurethanes,and combinations thereof, among others. Foamed or honeycomb structurescan also be useful.

Other factors which effect the stability and life of the storage mediarelate to dimensional stabilities and hygrothermal properties. Asubstrate with thermal and moisture dimensional stabilities attemperatures within the storage and operating temperature range of thestorage media should be employed with thermal and moisture stabilitiesat temperatures of about −6° C. (21° F.) to about 40° C. (104° F.)typically acceptable, stabilities within temperatures of about −12° C.(10° F.) to about 80° C. (175° F.) preferred, and stabilities withintemperatures of about −16° C. (3° F.) to about 100° C. (212° F.)especially preferred. Due to the varied environments in which thestorage media may be employed or stored, the storage media preferablyhas: (1) a heat distortion temperature greater than about 60° C. (140°F.), with greater than about 80° C. preferred; (2) creep characteristicspreferably equal to or better than that of bisphenol-A basedpolycarbonate resin; and (3) good hygrothermal properties such that thesubstrate does not significantly change shape, such as bow or warp.Preferably, the substrate's moisture content varies less than about 1.0%at equilibrium, with less than about 0.5% at equilibrium more preferred,and less than about 0.3% at equilibrium especially preferred, under testconditions of 80° C. at 85% relative humidity after 4 weeks.

In order to address the above design issues, this substrate can behomogenous or non-homogenous, and can have numerous geometries. Thehomogenous substrate can be a plastic which is substantially solid ormay contain a varying degree of porosity or one or more cavities (seeFIGS. 15, 16 17, and 33 to 35). As is illustrated in these Figures, thedensity of the substrate can be reduced by employing one or more hollowcavities (holes, bubbles, ribs, passageways, webs, etc.) within thesubstrate while maintaining a sufficiently smooth surface either bycontaining the cavities within the substrate or by utilizing a coatingover the substrate in the area of the storage media where the data willbe stored.

The size, shape, and location of the cavities is based upon the abovementioned design criteria. For example, referring to FIG. 17, thecavities may be located near the outer diameter of the substrate suchthat the central area of the substrate, which may be secured to the hubof the media read/write system, has the maximum yield strength while theouter periphery of the substrate has reduced density and inertialissues. As can be seen in FIGS. 8 to 14, and 33 to 35, the cavity canhave various geometries (linear, curved, convex, concave,convexo-concave, concavo-concave, convexo-convex, and the like), sizes(width, length and height), and locations throughout the substrate(intermittent, from the inner diameter to the outer diameter, or anylocation therebetween), and can be interconnecting or separate.

The non-homogenous substrate can be a plastic with a filler, core, orother reinforcement or insert, or may be a composite material, orcombinations thereof (see FIGS. 8 to 27). As is shown in the variousdrawings and as stated below in greater detail, the material geometry,location, and size of the insert/core/reinforcement can be adjusted toaddress the various design criteria; such as interconnecting orseparate, solid or non-solid, plates, web designs, hub designs,stiffening structures, inner diameter and/or outer diameter inserts,top, middle, bottom, or offset designs, finger or directional design,concentric stiffeners, partial surface, welded, bonded, or encapsulated;or combinations comprising at least one of the foregoing.

Referring to FIGS. 22 to 24, for example, a substrate can have areinforcement that comprises substantially all of the volume of thesubstrate such that the majority of the plastic is merely disposed nearthe surface of the substrate, e.g., as a thin film. In this embodiment,the core, which forms the majority of the substrate, can have athickness up to about 2.5 mm, with a thickness of about 0.75 mm to about2.0 mm preferred, and about 0.8 mm to about 1.2 mm especially preferred.As is illustrated, the thin plastic film can be disposed on one or bothsides of the core (e.g., metal, ceramic, glass, or the like). Typicallya plastic film having a thickness of about 50μ or less can be employed,with a thickness of about 20μ or less preferred.

Regardless of whether the substrate is homogenous or non-homogenous,contains hollow or filled cavities, or reinforcement, its geometry aswell as the geometry of the core/insert/reinforcement, can also beadjusted, interchangeably, to address various of the design factors.Referring to FIGS. 8 to 35, various substrate and core/insertgeometries, respectively, include substantially constant thickness,tapering on one or both sides, convex or concave on one or both sides,or combinations comprising at least one of the foregoing.

Adjusting the geometry of the substrate enables manipulation of themoment of inertia of the substrate when rotating, and control of themodal responses, i.e. the harmonics thereof. For example, various modalshapes (as shown in FIG. 36) can be obtained and avoided, based uponsectional variations in density through planar and/or radial thickness.As stated above, the preferred design is a substrate having a firstmodal resonance frequency outside of the frequency range for which thestorage media is designed.

Another manner of addressing the various design criteria for the storagemedia is addressing its use, such as its operating rotational speedwhich effects the speed in which data can be stored/retrieved.Conventionally, during use, storage media has been rotated at a constantspeed. The media is brought to its operating rotational speed prior toany reading or writing. However, the storage media can be rotated at avaried speed where the speed increases during peak use periods whiledecreasing during normal use periods; or rotational speed can be variedin order to maintain constant linear velocity at different areas of thedisk (e.g., inner vs. outer diameter). Such operating criteria will bothconserve energy and potentially render some design criteria moreimportant. Such criteria include, e.g., moment of inertia, modulus,density, viscoelasticity, thickness, and/or diameter to name a few.Storage media devices that change speeds make many of these criteria,e.g., moment of inertia and density, etc. of increased importance ascompared to constant speed devices.

In theory, any plastic that exhibits appropriate properties and can beemployed as the substrate, core, and/or coating. However, the plasticshould be capable of withstanding the subsequent processing parameters(e.g., application of subsequent layers) such as sputtering (i.e.temperatures up to and exceeding about 200° C. (typically up to orexceeding about 300° C.) for magnetic media, and temperatures of aboutroom temperature (about 25° C.) up to about 150° C. for magneto-opticmedia). That is, it is desirable for the plastic to have sufficientthermal stability to prevent deformation during the deposition steps.For magnetic media, appropriate plastics include thermoplastics withglass transition temperatures of at least 140° C. can be used, withgreater than about 150° C. preferred, and greater than about 200° C.more preferred (e.g., polyetherimides, polyetheretherketones,polysulfones, polyethersulfones, polyetherethersulfones, polyphenyleneethers, polyimides, high heat polycarbonates, etc.); with materialshaving glass transition temperatures greater than about 250° C. morepreferred, such as polyetherimide in which sulfonedianiline oroxydianiline has been substituted for m-phenylenediamine, among others,as well as polyimides, such as Probimide (or the dry powder equivalent,Matrimid 5218, from Ciba Geigy Chemical); combinations comprising atleast one of the foregoing, and others.

Additionally, it is possible for thermosets to be used in theapplication provided the thermoset possess sufficient flow under thestamping conditions to permit formation of the desired surface features.As various applications may require polymers with different glasstransition temperatures, it may be advantageous to be able to adjust theglass transition temperature of a plastic (homopolymer, copolymer, orblend) to achieve a film with the desired glass transition temperature.To this end, polymer blends, such as those described in U.S. Pat. No.5,534,602 (to Lupinski and Cole, 1996), may be employed in thepreparation of the coating solution. In this example, polymer blendsprovide, selectively, variable glass transition temperatures of about190° C. to about 320° C.

Some possible examples of plastics include, but are not limited to,amorphous, crystalline and semi-crystalline thermoplastic materials:polyvinyl chloride, polyolefins (including, but not limited to, linearand cyclic polyolefins and including polyethylene, chlorinatedpolyethylene, polypropylene, and the like), polyesters (including, butnot limited to, polyethylene terephthalate, polybutylene terephthalate,polycyclohexylmethylene terephthalate, and the like), polyamides,polysulfones (including, but not limited to, hydrogenated polysulfones,and the like), polyimides, polyether imides, polyether sulfones,polyphenylene sulfides, polyether ketones, polyether ether ketones, ABSresins, polystyrenes (including, but not limited to, hydrogenatedpolystyrenes, syndiotactic and atactic polystyrenes, polycyclohexylethylene, styrene-co-acrylonitrile, styrene-co-maleic anhydride, and thelike), polybutadiene, polyacrylates (including, but not limited to,polymethylmethacrylate, methyl methacrylate-polyimide copolymers, andthe like), polyacrylonitrile, polyacetals, polycarbonates, polyphenyleneethers (including, but not limited to, those derived from2,6-dimethylphenol and copolymers with 2,3,6-trimethylphenol, and thelike), ethylene-vinyl acetate copolymers, polyvinyl acetate, liquidcrystal polymers, ethylene-tetrafluoroethylene copolymer, aromaticpolyesters, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidenechloride, tetrafluoroethylene fluorocarbon polymers (Teflons), as wellas thermosetting resins such as epoxy, phenolic, alkyds, polyester,polyimide, polyurethane, mineral filled silicone, bis-maleimides,cyanate esters, vinyl, and benzocyclobutene resins, in addition toblends, copolymers, mixtures, reaction products and compositescomprising at least one of the foregoing.

Filler/reinforcement/core materials can be any material compatible withthe plastic and the ultimate environment in which the storage media willbe employed, which can be secured within or to the plastic, or which theplastic can be coated over, to produce the desired surface quality inthe area of data storage, and which provides the additional desiredmechanical strength to the substrate. Possible materials include: glass(such as silica, low melt glasses, etc.), foams and other low densitymaterials, carbon, metals (such as aluminum, tin, steel, platinum,titanium, metal matrices, others and combinations and alloys comprisingat least one of the foregoing), organic and inorganic materials,ceramics (e.g. SiC, Al₂O₃, etc.) thermoplastics, thermosets, rubbers,among others and composites, alloys and combinations comprising at leastone of these materials. These materials can be in the form of particles,bubbles, microspheres or other hollow fillers, fibers (long, short,continuous, chopped, etc.), mesh, woven, non-woven, preforms, inserts,plates, disks, others and combinations comprising at least one of theforegoing, of various sizes and geometries. For example, FIGS. 33 to 35show a few of the possible core/insert geometries with the polymericmaterial comprising a thin (e.g., less than about 50μ) coating or thick(e.g., greater than about 50μ) coating over the core/insert. Glass,metal, metal matrix composites, and carbon cores are typically preferredfor some applications where elevated temperatures may be a factor, dueto the reduced thermal decay of stiffness in substrates containing thesematerials.

The amount of filler employed is dependent upon the desired substratemechanical properties and the fillers effects on the substrates′harmonics, surface quality, and inertial factors. The filler (particles,cavity, bubbles, core, inserts, etc.) can occupy up to as much as 99.9%or more of the volume (vol %) of the substrate, with about 5 vol % toabout 50 vol % occupied by the filler more common, and about 85 vol % toabout 99 vol % occupied by the filler preferred in some alternateembodiments.

Numerous methods can be employed to produce the storage media includinginjection molding, foaming processes, sputtering, plasma vapordeposition, vacuum deposition, electrodeposition, extrusion coating,spin coating, spray coating, meniscus coating, data stamping, embossing,surface polishing, fixturing, laminating, rotary molding, two shotmolding, co-injection, over-molding of film, microcellular molding, aswell as other techniques, and combinations comprising at least one ofthe foregoing. Preferably the technique employed enables in situproduction of the substrate having the desired surface features, (e.g.,servo-patterning (such as pits and grooves), bit patterning, edgefeatures, protrusions, asperities (e.g., laser bumps, and the like),R_(a), etc.).

One possible process comprises an injection molding-compressiontechnique where a mold is filled with a molten plastic. The mold maycontain a preform, inserts, fillers, etc. The plastic is cooled and,while still in an at least partially molten state, compressed to imprintthe desired surface features (e.g., pits, grooves, edge features,smoothness, and the like), arranged in spiral concentric or otherorientation, onto the desired portion(s) of the substrate, i.e. one orboth sides in the desired areas. The substrate is then cooled to roomtemperature.

For optical or magnetic data storage on a substrate, information storedis often stored on the surface of the substrate. This information may beimprinted directly onto the surface (as in the case of a CD), or storedin a photo- or magnetically-definable medium, which has been depositedonto the surface of substrate (e.g., “Winchester” hard disk drive). Dueto the surface quality requirements of such systems, disks (metal,ceramic, glass, etc.) were coated with nickel phosphide (NiP), forexample, and then polished to obtain the desired surface quality.However, polishing is an expensive and laborious process. Additionally,these substrates do not traditionally offer the capability of imprintingfeatures onto the surface, even though such features, e.g., pits orgrooves, may be desirable for use as geographic locators, such as asector map. Typically these geographic locators have a depth of up toabout 30 nanometers (nm) or more, with about 20 nm to about 30 nmgenerally preferred.

In one embodiment, a metal, glass, ceramic, or other substrate to whicha plastic layer has been applied exhibits both the desired mechanicalproperties and the ability to have surface features imprinted into thesurface. The plastic layer can be deposited by a variety of techniques,including spin coating, vapor deposition (e.g. plasma enhanced chemicalvapor deposition), electrodeposition coating, meniscus coating, spraycoating, extrusion coating, and the like, and combinations comprising atleast one of the foregoing.

Spin coating comprises preparing a solution of a plastic precursor(e.g., monomer or oligomer) or the plastic itself (where a solvent canbe employed, or one of the monomers can act as the solvent). The disk tobe coated is secured to a rotatable surface and a portion of plasticsolution is dispensed near the center of the substrate. Alternately, abead of the plastic solution is deposited in a ring like geometry, alongthe inner boundary of disk where the coating is to be located. The diskis then spun at a sufficient rate to, via centrifugal forces, spread theplastic solution across the surface of the disk. Finally, if applicable,the coating is dried and cured.

In order to improve adhesion of the coating to the substrate,optionally, an adhesion promoter, such as an organosilane or anotherconventional adhesion promoter, can be used. Possible organosilanesinclude VM-651 and VM-652 commercially available from DuPont. If anadhesion promoter is employed, it is typically dissolved in a solvent,such as methanol, water, and combinations comprising at least one of theforegoing, and is applied to the disk prior to applying the plasticbead. Once the adhesion promoter is spin coated onto the disk, theplastic coating is applied as described above.

For example, a polyetherimide resin, such as Ultem® resin grade 1000,commercially available from GE Plastics, is dissolved inanisole/gamma-butyrolactone solvent system (15% Ultem® resin by weight(wt %)). A rigid substrate (metal, polymer, glass, or other), which isoptionally polished, is placed on a rotatable device, commonly referredto as a spinner, and held in place via a mechanical device or a vacuum.An adhesion promoter, such as 5 ml of 0.05% solution VM651 (an adhesionpromoter commercially available from DuPont) in water/methanol solution,is applied by dispensing it onto the spinning or stationary substrate.The substrate is then, preferably, spun to distribute the adhesionpromoter, such as at a rate of about 2,000 rpm for about 30 seconds. Ifan adhesion promoter is employed, the substrate can optionally berinsed, such as with methanol, to remove excess adhesion promoter, anddried (e.g., air dried, vacuum dried, heat dried, or the like), prior tothe application of the plastic solution.

Once the rigid substrate has been prepared, plastic solution can beapplied to the substrate around the inner diameter of the area to becoated, while optionally masking areas that are not to be coated. Thesubstrate is spun to substantially uniformly spread the plastic solutionacross the substrate, forming a film. The thickness of the film isdependent upon various parameters, e.g., the quantity of plasticsolution, the desired thickness, the viscosity of the plastic solution,the spin rate, the spin duration, plastic solution solids content, andenvironmental conditions (including temperature, humidity, atmospheretype (e.g. inert gas), and atmospheric pressure), among others. Althougha thickness below about 0.1 micrometers (μ) can be attained, the film ispreferably sufficiently thick to afford a planar surface overundesirable surface imperfections in the substrate and to allow desiredsurface features (e.g., pits, grooves, etc.) to be placed onto the film.Typically, a thickness of about 0.5μ or greater is generally preferred,with a thickness of up to about 50μ possible, up to about 20μ preferred,and about 0.5μ to about 10μ especially preferred for storage media typeapplications. Determination of a final thickness range will vary, inpart, by the desired depth of any features to be placed onto the film aswell as the surface imperfections on the rigid substrate that need to bemasked by the film.

With respect to spin duration and rate, which must be sufficient todisperse the plastic solution across the substrate in the desired area,these parameters are chosen based on factors including, e.g., theplastic solution viscosity and solids content, and the desired coatingthickness; all interdependent parameters. Typically, however, the spinrate is greater than about 1,000 revolutions per minute (rpm) for up toabout 5 minutes or more, with greater than about 1,500 rpm for less thanabout 2.5 minutes preferred, and greater than about 1,800 rpm for lessthan about 1.5 minutes especially preferred. For example, a 3μ thickcoating can be applied using plastic solution containing 15 wt % Ultem®resin grade 1000 in anisole/gamma-butyrolactone solvent, and a spin rateof 2,000 rpm for a duration of 25 seconds.

Once the coating as been dispersed across the substrate, it can becured, preferably in an inert atmosphere, such as nitrogen, for asufficient period of time to remove the solvent and polymerize thepolymer precursor (if necessary) and at a rate effective to obtain thedesired surface quality. The coated substrate can be raised to thedesired temperature at a rate such that the solvent removal doesn's havedeleterious effects on the surface features. For example, the coatedsubstrate can be heated to greater than about 200° C., with about 300°C. or greater typically preferred, at a rate of up to about 10 degreesper minute (deg/min), with a rate of up to about 5 deg/min preferred,and a rate of less than about 3 deg/min especially preferred. Once thesubstrate has attained the desired temperature, it is maintained at thattemperature for a sufficient period of time to remove the solvent and,if necessary, to polymerize the polymer precursor, and is then cooled.Typically a period of up to several hours is employed, with less than 2hours preferred, and a rate of minutes or portions thereof especiallypreferred. A substrate prepared in this manner, optionally withsubsequent processing, can be used for data storage applications, suchas magnetic hard drives.

Alternatively, the substrate (entire substrate or coating on the core)can be cured using microwave technology. Preferably, a variablefrequency microwave curing system is employed. The substrate enters themicrowave area where the sweep rate, power, bandwidth, and centralfrequency are adjusted for the particular substrate such that themicrowave selectively heats the polymer without substantially effectingthe core, if desired.

Other possible curing techniques include using ultraviolet light toinitiate a crosslinking reaction, radiative heating (placing the samplein close proximity to a hot surface), contact heating (sample is inphysical and therefore thermal contact with a hot fixture), rapidthermal annealing (employing a heat source such as a coil or the like,or a lamp such as quartz or the like, which is heated at a very rapidrate, such as greater than 10 degrees per second), inductive heating(e.g., with radio frequency), and the like, as well as combinationscomprising at least one of the foregoing.

In conjunction with the above curing techniques, other processingmethods may be employed to facilitate the curing process, to removesolvent, and/or to improve the quality of the product. Possibleadditional processing methods include: employing a vacuum, usingstripping agents (e.g., inert gasses, inert volatile solvents,azeotropes, and the like), drying agents, and other conventionalmethods, as well as combinations comprising at least one of theforegoing.

Alternatively, the curing time can be based upon economies and thedesired surface features (pits, grooves, asperities (e.g. laser bumps),edge features, and/or smoothness) can be disposed on the surfacesubsequent to curing. Following application, if applicable, the plasticfilm is cured (thermal, ultraviolet, etc.), and, optionally, the desiredsurface features are formed by photolithography (including, but notlimited to dry etch), laser ablation through direct write or wideexposure with the use of photomasks, hot or cold stamping, embossing, orother techniques.

Putting the surface features on the substrate by employingphotolithography can be accomplished with any conventionalphotolithography technique, such as those which employ reactive ionetching, plasma, sputtering, and/or liquid chemicals or chemical vaporsto etch the polymer coating. Conventional photolithographic techniques,e.g., nanoimprint lithography, used to prepare contact probe datastorage devices are useful; however, care must be taken to retainsufficient plastic film depth within the surface feature to provide thedesired planarity of the surface of the rigid substrate.

Generally, embossing is preferred since the substrate is either plasticor at least comprises a thin plastic film on the embossing surface. Notto be limited by theory, due to the rheology of the plastic material,not only can pits, grooves, and edge features be embossed into thesubstrate, but the desired surface quality can also be embossed (e.g.,desired smoothness, roughness, microwaviness, and flatness). In apreferred embodiment, embossed bit-patterns and/or servo-patterns have adepth of about 10 nm to about 150 nm, preferably about 20 nm to about 50nm. Depths shallower than about 10 nm can result in features that arenot accurately recognized by the head device. Conversely, deeperfeatures or features that vary outside the ranges can result inundesirable head-disk interactions.

Embossing, can be accomplished using conventional techniques.Alternatively, a unique embossing technique can be employed where asubstrate, such as a disk having a plastic surface, is embossed bypreheating a mold. The mold should be heated to a temperature that, inconjunction with the temperature of the substrate, is capable ofembossing the desired surface features onto the plastic surface of thesubstrate. The mold temperature can be at, above, or below the glasstransition (Tg) temperature of the material to be embossed. If thetemperature is above such glass transition temperature, it is preferredthe mold temperature be within about 30° C. of the glass transitiontemperature of the material, with a temperature within about 15° C.preferred, and a temperature within about 10° C. especially preferred;with the mold being preheated to a temperature below the glasstransition temperature of the material to be embossed even morepreferred. In an especially preferred embodiment, the mold is preferablyheated to within a few degrees below the glass transition temperaturefor crystalline materials, and at a temperature within at least about 5°C., preferably within at least about 10° C. or greater for amorphousmaterials.

In addition to heating the mold, the substrate is heated to atemperature greater than the glass transition temperature of thematerial to be embossed. The substrate is heated to the materialtemperature required to facilitate replication of the geographiclocators and/or other surface features on the substrate. Typically, thesubstrate is heated to about 5° C. above the glass transitiontemperature or less for crystalline material, with greater than about 5°C. common for amorphous materials.

Once the substrate has attained the desired temperature, it is placed inthe mold and pressure is applied. After placing the substrate in themold the temperature thereof can be maintained, increased or decreasedas necessary in order to optimize replication and enable substraterelease from the mold while maintaining the integrity of the surfacefeatures. Typically in order to maintain the integrity of the surfacefeatures, the molded substrate is cooled to below the glass transitiontemperature prior to removal from the mold.

By preheating to and maintaining the mold at a temperature below theglass transition temperature of the material, the time required forheat-up and cool-down of conventional embossing processes issignificantly diminished, especially in relation to processing numeroussubstrates. For example, numerous substrates are heated to a temperatureabove the glass transition temperature of the material to be embossed.Meanwhile the mold is heated to and maintained at a temperature belowthe glass transition temperature. A substrate is then placed in the moldand is embossed while the mold cools the substrate (due to thetemperature differential). The substrate can then be removed from themold and the next substrate placed in the mold. It is not necessary toheat the substrate and the mold to above the glass transitiontemperature and then to cool the combination to below the glasstransition temperature as is conventional. Conventional embossingtechniques typically take about 6 to 12 hours to complete, while theabove embossing techniques can be accomplished in minutes.

For example, an aluminum disk coated with polyetherimide (Ultem® resingrade 1010) is fixtured to a spindle and heated to about 780° F. (415°C.) in a furnace oven. An embossing mold having the desired surfacefeature negative is heated to about 205° C. Once the disk is attemperature it is loaded into the mold and, while cooling (due to thetemperature of the mold) compressed under a time-pressure profile toemboss the surface features into the substrate surface. The embossedsubstrate is then removed from the mold.

By maintaining the mold below or slightly above the glass transitiontemperature and separately heating the substrate to greater than theglass transition temperature, the embossing cycle time can be reduced byorders of magnitude.

Once the substrate has been coated with polymer, and formed with theappropriate surface features, if desired various layers can then beapplied to the substrate through one or more conventional techniques,e.g., sputtering, chemical vapor deposition, plasma-enhanced chemicalvapor deposition, reactive sputtering, evaporation, and the like. Forexample, in some cases, high areal density storage media might have pitsand grooves on the polymer substrate that can be solely geographiclocators; i.e. they are not required to store data therein. The data isstored in data storage layer(s). Furthermore, the data stored in thedata storage layer(s) may be changed (rewritten) by repeating theimpinging step at higher densities than conventional, i.e. “low” densitycompact disks.

The layers applied to the substrate may include one or more data storagelayer(s) (e.g., magnetic, magneto-optic, etc.), protective layer(s),dielectric layer(s), insulating layer(s), combinations thereof andothers. The data storage layer(s) may comprise any material capable ofstoring retrievable data, such as an optical layer, magnetic layer, ormore preferably a magneto-optic layer, having a thickness of up to about600 Å, with a thickness up to about 300 Å preferred. Possible datastorage layers include, but are not limited to, oxides (such as siliconeoxide), rare earth element—transition metal alloy, nickel, cobalt,chromium, tantalum, platinum, terbium, gadolinium, iron, boron, others,and alloys and combinations comprising at least one of the foregoing,organic dye (e.g., cyanine or phthalocyanine type dyes), and inorganicphase change compounds (e.g., TeSeSn or InAgSb). Preferably, the datalayer has a coercivity of at least about 1,500 oersted, with acoercivity of about 3,000 oersted or greater especially preferred.

The protective layer(s), which protect against dust, oils, and othercontaminants, can have a thickness of greater than 100μ to less thanabout 10 Å, with a thickness of about 300 Å or less preferred in someembodiments. In another embodiment, a thickness of about 100 Å or lessis especially preferred. The thickness of the protective layer(s) isusually determined, at least in part, by the type of read/writemechanism employed, e.g., magnetic, optic, or magneto-optic.

Possible protective layers include anti-corrosive materials such asnitrides (e.g., silicon nitrides and aluminum nitrides, among others),carbides (e.g., silicon carbide and others), oxides (e.g., silicondioxide and others), polymeric materials (e.g., polyacrylates orpolycarbonates), carbon film (diamond, diamond-like carbon, etc.) amongothers, and combinations comprising at least one of the foregoing.

The dielectric layer(s) which are often employed as heat controllers,can typically have a thickness of up to or exceeding about 1,000 Å andas low as about 200 Å. Possible dielectric layers include nitrides(e.g., silicon nitride, aluminum nitride, and others); oxides (e.g.,aluminum oxide); carbides (e.g., silicon carbide); and combinationscomprising at least one of the foregoing, among other materialscompatible within the environment and preferably, not reactive with thesurrounding layers.

The reflective layer(s) should have a sufficient thickness to reflect asufficient amount of energy to enable data retrieval. Typically thereflective layer(s) can have a thickness of up to about 700 Å, with athickness of about 300 Å to about 600 Å generally preferred. Possiblereflective layers include any material capable of reflecting theparticular energy field, including metals (e.g., aluminum, silver, gold,titanium, and alloys and mixtures comprising at least one of theforegoing, and others). In addition to the data storage layer(s),dielectric layer(s), protective layer(s) and reflective layer(s), otherlayers can be employed such as lubrication layer and others. Usefullubricants include fluoro compounds, especially fluoro oils and greases,and the like.

One unexpected result of the storage media described herein that containa rigid substrate, e.g., an aluminum substrate, with a plastic resinembossed with surface features, was retention of head slap performanceas compared to conventional storage media. Conventional aluminum mediaare typically coated, e.g., with nickel phosphide, to improve thesurface hardness for polishing and to resist damage to the polishedsurface by contact with the head. Plastic resins are generally softerthan the aluminum surface coating and would be expected to limit thehead slap resistance of the storage media; however, storage mediadescribed herein containing plastic films unexpectedly exhibited noobserved diminished slap resistance. This unexpected result is believedto depend somewhat on the thickness of the plastic film and plasticfilms having higher thickness are expected to have diminished head slapresistance. Thus, in an especially preferred embodiment, the head slapresistance of a coated aluminum substrate having a plastic film,preferably containing surface features, is substantially equivalent tothe head slap resistance of the coated aluminum substrate not containingthe plastic film. Similar head slap results can be obtained with otherrigid substrates such as glass.

The storage media described herein can be employed in conventionaloptic, magneto-optic, and magnetic systems, as well as in advancedsystems requiring higher quality storage media and/or areal density.During use, the storage media is disposed in relation to a read/writedevice such that energy (magnetic, light, a combination thereof oranother) contacts the data storage layer, in the form of an energy fieldincident on the storage media. The energy field contacts the layer(s)disposed on the storage media prior to (if ever) contacting thesubstrate. The energy field causes some physical or chemical change inthe storage media so as to record the incidence of the energy at thatpoint on the layer. For example, an incident magnetic field might changethe orientation of magnetic domains within the layer, or an incidentlight beam could cause a phase transformation where the light heats thematerial.

For example, referring to FIG. 2, in a magneto-optic system 100, dataretrieval comprises contacting the data storage layer(s) 102 with apolarized light 110 (white light, laser light, or other) incident onsuch layer(s). A reflective layer 106, disposed between the data storagelayer 102 and substrate 108, reflects the light back through the datastorage layer 102, the protective layer 104, and to the read/writedevice 112 where the data is retrieved.

In another embodiment, referring to FIG. 3, the read/write device 112detects the polarity of magnetic domains in the disk storage layer 102′(i.e. data is read). To write data onto the storage media, a magneticfield is imposed onto the data storage layer 102′ by the read/writedevice 112. The magnetic field passes from the read/write device 112′,through the lubrication layer 105, and the protective layer 104 to themagnetic layer 102′, forming magnetic domains aligned in either of twodirections and thereby defining digital data bits.

The following examples are provided to further illustrate the presentinvention and are not intended to limit the scope thereof.

EXAMPLES Example 1

A substrate with outer diameter of 130 mm and thickness of 1.2 mm wasformed out of a polyetherimide resin (Ultem® resin grade 1010 obtainedfrom GE Plastics) using injection molding under standard conditionsknown in the art. The surface smoothness of the substrate was less than10 Å R_(a), and the first modal frequency was about 175 Hz. At thisfrequency, the axial displacement was about 0.889 mm. The benefitscompared to the prior art (Comparative Example #1) are clear.

Example 2

A substrate with dimensions of 130 mm diameter and 1.2 mm thickness canbe produced by injection molding of polycarbonate filled with 20 wt %carbon fiber. The material will exhibit a flexural modulus of 1.6million psi, a mechanical damping coefficient of 0.015, and specificgravity of 1.29 g/cc. The storage media will demonstrate a maximum axialdisplacement of 0.32 mm during vibrational excitation, and a first modalfrequency of 302 Hz.

Example 3

A substrate with outer diameter of 95 mm and thickness of 2 mm wasformed with a core of polyphenylene ether/polystryrene (PPE/PS)containing 20 wt % ceramic microfibers and a skin of PPE/PS (40/60) byco-injection molding. The microfibers, with average dimensions on theorder of 10-20μ length×0.3-0.6μ diameter) were significantly smallerthan conventional carbon fibers. The surface smoothness of the substratewas improved by approximately a factor of 2 compared to the conventionalcarbon fiber co-injected disk, and the first modal frequency was about425 Hz. At this frequency, the axial displacement was about 0.15 mm. Thebenefits compared to the prior art (Comparative Examples #1) are clear.

Example 4

A substrate with outer diameter of 130 mm and thickness of 1.2 mm wasformed with a core of 20 wt % carbon fiber-filled polycarbonate and askin of pure polycarbonate using co-injection molding with a thicknessratio of about 1 unit of core to 1 unit of skin under standardconditions known in the art. The surface smoothness of the substrate wasabout 10 Å R_(a) and the first modal frequency was about 210 Hz. At thisfrequency, the axial displacement was about 1.27 mm; however, thedisplacement and frequency can be changed with changes in the core toskin ratio. The benefits compared to the prior art (Comparative Example#1) are clear.

Example 5

A substrate with outer diameter of 120 mm and thickness of 0.9 mm isformed out of polycarbonate containing 30 wt % carbon fiber, 21 wt %poly(styrene-isoprene), and 3.5 wt % poly(styrene-maleic anhydride) (allbased upon the total weight of the composition) using injection moldingusing standard conditions known in the art. The first modal frequency isabout 292 Hz. At this frequency, the axial displacement is about 0.069mm. The benefits compared to the prior art (Comparative Examples #1 and#2) are clear.

Example 6

A substrate with outer diameter of 95 mm and thickness of 2 mm is formedwith a core of polycarbonate containing 30 wt % carbon fiber, 21 wt %poly(styrene-isoprene) vibration dampening filler, and 3.5 wt %poly(styrene-maleic anhydride) and skin of polycarbonate (all based uponthe total weight of the composition) using co-injection molding understandard conditions known in the art. The core comprises about 50% ofthe thickness of the disk. The surface smoothness of the substrate isabout 1.3 nm R_(a) and the first modal frequency is about 450 Hz. Atthis frequency, the axial displacement is about 0.033 mm. The benefitscompared to the prior art (Comparative Examples #1 and #2) are clear.

Example 7

A substrate with outer diameter of 130 mm and thickness of 1.2 mm isformed with a core of polycarbonate containing 20 wt % carbon fiber and10 wt % poly(styrene-isoprene) (all based upon the total weight of thecomposition) and a skin of polycarbonate by injection molding the filledmaterial in a mold that contains polycarbonate film on one or both sidesof the mold. The surface smoothness of the substrate is about 1 nm R_(a)and the first modal frequency is about 250 Hz. At this frequency, theaxial displacement is about 0.20 mm. The benefits compared to the priorart (Comparative Examples #1 and #2) are clear.

Example 8

A substrate with outer diameter of 130 mm and thickness of 1.2 mm isformed with a core of polycarbonate containing 30 wt % carbon fiber in amold that contains polycarbonate film on one or both sides of the mold.The surface smoothness of the substrate is about 1 nm R_(a) and thefirst modal frequency is about 300 Hz. At this frequency, the axialdisplacement is about 0.40 mm. The benefits compared to the prior art(Comparative Example #1) are clear.

Example 9

A thin layer (5μ) of polyetherimide was electrochemically deposited ontoone or both sides of an aluminum substrate. Subsequently, geographiclocators (pits) were formed into the surface of the polyetherimide filmusing a hot stamping technique. This substrate was superior to atraditional aluminum substrate (Comparative Example #2) in that itcontains the desirable pit structure of geographic locators and othersurface features formed through embossing.

Example 10

A thin layer of polyetherimide (5μ) was deposited by spin coating apolymer containing solution onto one side of an aluminum substrate. Thissubstrate was superior to a traditional aluminum substrate (ComparativeExample #2) in that the final surface was smooth enough (less than 10 ÅR_(a) and total surface flatness less than 8μ) for use in magnetic datastorage applications, but the substrate did not have to undergo theplating and polishing steps used in the preparation of conventionalmetal or ceramic substrates. Upon deposition of a sputtered magneticdata layer, magnetic coercivity greater than 2,500 oersted was achieved.

Example 11

A thin layer of polyetherimide (5μ) was deposited by spin coating apolymer containing solution onto one side of a glass substrate. Thefinal surface had less than 10 Å R_(a) and total surface flatness lessthan 8μ. Upon deposition of a sputtered magnetic data layer, magneticcoercivity greater than 3,000 oersted was achieved. The coated substrateshowed no damage after a standard 800 G head slap test.

Example 12

A thin layer of polyetherimide can be deposited by spin coating apolymer containing solution onto one or both sides of an aluminum-boroncarbide rigid substrate. This substrate would be superior to atraditional aluminum substrate (Comparative Example #2) in that thematerial would have a significantly higher specific modulus. It would besuperior to aluminum-boron carbide substrates without a coating in thatthe coating makes the surface smooth enough for use in magnetic datastorage applications. (Using conventional means, such as polishing, itis difficult, if not impossible, to achieve adequate surfacesmoothness.)

Example 13

A thin layer of polyetherimide was deposited onto one side of analuminum substrate by spin coating a polymer-containing solution ontothe surface(s) and curing. Subsequently, surface features were formedinto the surface using an embossing technique, e.g., a hot stamping.This substrate was superior to a traditional aluminum substrate(Comparative Example #2) in that it contained the desirable pitstructure of geographic locators and the desired surface quality; e.g.,less than 10 Å R_(a).

Example 14

A substrate with outer diameter of 130 mm and thickness of 1.2 mm andcontaining microporosity can be formed out of polycarbonate (Lexan®resin grade OQ1030L obtained from GE Plastics) using the Mucellmicrocellular injection molding process. The substrate would show 20%lower moment of inertia and higher modal frequency compared toComparative Example #1.

Example 15

A substrate with outer diameter of 130 mm and thickness of 1.2 mm andcontaining a microporous and smooth polycarbonate skin can be formed outof polycarbonate (Lexan® resin grade OQ1030L obtained from GE Plastics)using the Mucell microcellular injection molding process in a mold thatcontains polycarbonate film on one or both sides of the mold. Thesubstrate would demonstrate the same benefits of reduced moment ofinertia and higher modal frequency of Example #13 with reduced surfaceroughness.

Example 16

A substrate with outer diameter of 130 mm and thickness of 1.2 mm wasformed out of polyetherimide (Ultem® resin grade 1010 obtained from GEPlastics) filled with about 60 wt % of a low melting (less than 400° C.)glass filler (Coming Cortem) using injection molding under standardconditions known in the art. The first modal frequency was about 210 Hz.At this frequency, the axial displacement was about 0.723 mm. Thebenefits compared to the prior art (Comparative Example #1) are clear.

Example 17

A substrate with outer diameter of 120 mm and thickness of 1.2 mm wasformed out of styrene-acrylonitrile copolymer (SAN CTS100 obtained fromGE Plastics) using injection molding under standard conditions known inthe art. The substrate showed reduced moment of inertia, improvedflatness, and higher modal frequency compared to Comparative Example #1.

Example 18

A substrate with outer diameter of 120 mm and thickness of 1.2 mm wasformed out of a 60/40 weight percent blend of poly(phenylene ether)resin and polystyrene using injection molding. The substrate showedreduced moment of inertia, improved flatness, and higher modal frequencycompared to Comparative Example 1.

Example 19

A substrate with outer diameter of 120 mm and thickness of 1.2 mm can beformed out of a 45/30/25 weight percent blend of poly(phenylene ether)resin, polystyrene, and polystyrene-co-(acrylonitrile) using injectionmolding. The substrate will show reduced moment of inertia, improvedflatness, and higher modal frequency compared to Comparative Example #1.

Example 20

A substrate with outer diameter of 120 mm and thickness of 1.2 mm out ofa 60/40 wt % blend of poly(phenylene ether) resin with polystyrene andcontaining 20 wt % of zinc sulfide particulate filler (all weights basedon the weight of the entire composition) using injection molding. Thesubstrate showed reduced moment of inertia, improved flatness, andhigher modal frequency compared to Comparative Example #1.

Example 21

A substrate with outer diameter of 120 mm and thickness of 1.2 mm wasformed out of a 60/40 weight percent blend of poly(phenylene ether)resin with polystyrene and containing 20 wt % of clay particulate filler(all weights based on the weight of the entire composition) usinginjection molding. The substrate showed reduced moment of inertia,improved flatness, and higher modal frequency compared to ComparativeExample #1.

Example 22

A substrate with outer diameter of 120 mm and thickness of 1.2 mm can beformed out of a 60/40 weight percent blend of poly(phenylene ether)resin with polystyrene and containing 20 wt % of zinc sulfideparticulate filler (all weights based on the weight of the entirecomposition) using injection molding in a mold containing a “managedheat transfer” insulating layer, as described in U.S. Pat. No.5,458,818. The substrate would show reduced moment of inertia, improvedflatness, and higher modal frequency compared to Comparative Example #1and improved replication of the mold surface compared to Example #20.

Example 23

A substrate can be prepared as in Example #15. The substrate was heldusing a clamping device that contained a viscoelastic washer (e.g.,elastomer) between the mount and the substrate. The structure showedreduced axial displacement (0.475 mm vs. 0.723 mm) at the first modalfrequency compared to the same substrate when clamped using a device notcontaining the elastomeric washer.

Comparative Examples Comparative example 1

A substrate with outer diameter of 130 mm and thickness of 1.2 mm wasformed out of a polycarbonate resin (Lexan® resin grade OQ1030L obtainedfrom GE Plastics) using injection molding. The surface smoothness of thesubstrate was less than about 10 Å R_(a) and the first modal frequencywas about 150 Hz. At this frequency, the axial displacement was about1.40 mm.

Comparative example 2

A substrate with outer diameter of 130 mm and thickness of 1.2 mm wasformed out of aluminum by punching the disk from an aluminum sheet,plating with nickel-phosphide, and polishing to achieve the desiredsurface roughness (less than 10 Å R_(a)). The first modal frequency wasabout 500 Hz. At this frequency, the axial displacement was about 0.075mm.

It should be clear from the examples and teachings provided herein thatnovel and/or enhanced storage media for data have been invented. In someembodiments, optical, magnetic, and/or magneto-optical media that are atleast in part made from plastic and having a high storage capability,e.g., areal density greater than about 5 Gbits/in², can be designed. Inother embodiments, storage media were unexpectedly provided having verydesirable properties, including at least one of, e.g., surface roughnessof less than about 10 Å R_(a), low microwaviness, edge-lift less thanabout 8μ, mechanical damping coefficient greater than about 0.04 at atemperature of 24° C., a resonant frequency of greater than about 250Hz, an axial displacement peak of less than about 500μ under shock orvibration excitation, a data layer with a coercivity of at least about1,500 oersted, and a Youngs modulus of at least about 7 GPa.

Some of the storage media described herein contain a rigid core with aspin coated, spray coated, electrodeposited, or combination thereof,plastic film or layer on one or both sides. The plastic may be athermoplastic, thermoset, or mixture thereof. In additional embodiments,the storage media has surface features (e.g., pits, grooves, edgefeatures, asperities (e.g., laser bumps, and the like), roughness,microwaviness, and the like) placed into the plastic (film, layer, core,substrate) preferably using an embossing technique (i.e., the substratecan be physically patterned). A further advantage of a physicallypatterned substrate is the elimination of the need for servo-patterning(pits, grooves, etc.) of the data layer. This can eliminate the timeconsuming process of servo-patterning the data layer; typically aseveral hour process. In addition, since the data layer can be wholly orsubstantially free of servo-patterning, the area of the data layeravailable for data storage is increased.

Unexpected results were also obtained in relation to further processingand mechanical properties. As is discussed above, the plastic withstoodthe deposition of additional layers (e.g., data layer(s), reflectivelayer(s), protective layer(s), etc.) using techniques such as sputteringat elevated temperatures, often at temperatures in excess of the glasstransition temperature of the plastic. Also, the hybrid storage mediacontaining a rigid substrate having a plastic film or layer attachedthereto retained head slap performance as compared to conventionalstorage media. These illustrative embodiments and results should beapparent to those of ordinary skill in the art from the description andexamples provided herein.

Unlike prior art storage media, this storage media employs a substratehaving at least a portion thereof plastic (e.g., at least a thin plasticfilm) to attain the desired mechanical properties and surface features.Due to the use of the plastic, in situ formation of the substrate withthe desired surface features is possible. Furthermore, surface features,including roughness, etc., can be embossed directly into the substratesurface, rendering production of this storage media cost effective. Afurther advantage is that the surface features have a greater than about90% replication of an original master.

1. A method for forming a data storage medium, comprising: injectionmolding a substrate comprising a plastic surface and a preformed core,wherein the plastic surface comprises surface features, wherein saidsurface features have greater than about 90% of a surface featurereplication of an original master; and disposing a reflective layer on asurface of the substrate; wherein said data storage medium has an axialdisplacement peak of less than about 500μ under shock or vibrationexcitation when excited by a 1 G sinusoidal loading; wherein the storagemedium has a thickness of up to about 1.2 mm.
 2. The method of claim 1,wherein said core comprises a material selected from the groupconsisting of metal, glass, ceramic, metal-matrix composite, and alloysand combinations comprising at least one of the foregoing materials. 3.The method of claim 1, wherein the plastic surface comprises athermoset.
 4. The method of claim 1, wherein the plastic surfacecomprises a polystyrene and comprises a material selected from the groupconsisting of polyphenylene ether, blends comprising polyphenyleneether, copolymers comprising polyphenylene ether, mixtures comprisingpolyphenylene ether, reaction products comprising polyphenylene ether,and composites comprising polyphenylene ether.
 5. The method of claim 1,further comprising disposing a thermoset coating wherein the plasticsurface is between the thermoset coating and the core.
 6. The method ofclaim 1, wherein the thickness is about 0.8 mm to about 1.2 mm.
 7. Themethod of claim 1, wherein the plastic surface is disposed around thepreformed core.
 8. The method of claim 1, wherein the preformed corecomprises a different material than the plastic surface.
 9. The methodof claim 1, wherein the plastic surface comprises a thermoset and thepreformed core comprises a material selected from the group consistingof a polystyrene and comprises a material selected from the groupconsisting of polyphenylene ether, blends comprising polyphenyleneether, copolymers comprising polyphenylene ether, mixtures comprisingpolyphenylene ether, reaction products comprising polyphenylene ether,and composites comprising polyphenylene ether.
 10. A method for forminga data storage medium, comprising: injection molding a substratecomprising a plastic surface and a preformed core, wherein the plasticsurface comprises surface features, wherein said surface features havegreater than about 90% of a surface feature replication of an originalmaster; disposing a reflective layer on the surface features; anddisposing a thermoset coating on the reflective layer; wherein said datastorage medium has an axial displacement peak of less than about 500μunder shock or vibration excitation when excited by a 1 G sinusoidalloading; and wherein the storage medium has a thickness of up to about1.2 mm.
 11. The method of claim 10, wherein the plastic surfacecomprises a thermoset and the preformed core comprises a materialselected from the group consisting of a polystyrene and comprises amaterial selected from the group consisting of polyphenylene ether,blends comprising polyphenylene ether, copolymers comprisingpolyphenylene ether, mixtures comprising polyphenylene ether, reactionproducts comprising polyphenylene ether, and composites comprisingpolyphenylene ether.